1. Field of the Invention
The present invention relates to a method of mounting a semiconductor chip, and in particular to a method of mounting a semiconductor chip by flip-chip bonding using ultrasonic vibration.
2. Related Art
When mounting a semiconductor chip onto a circuit board by flip-chip bonding, a method of mounting that applies ultrasonic vibration to the semiconductor chip is carried out. When mounting a semiconductor chip using ultrasonic vibration, there is a known problem that the bonding strength of the bonded parts depends on the applied direction of the ultrasound and the arrangement of the wiring patterns (bonding patterns) for mounting that are formed on the circuit board.
FIG. 6 is a plan view showing a state where a semiconductor chip 20 is flip-chip bonded on a circuit board 10 when looking from above, with the arrow showing the direction of vibration for the ultrasound.
FIG. 7A is a cross-sectional view showing one bonding pattern 12 (a bonding pattern in the part A in FIG. 6) whose longitudinal direction is parallel to the direction of vibration (the direction of the arrow) for the ultrasonic vibration, and FIG. 7B is a cross-sectional view showing one bonding pattern 12 (a bonding pattern in the part B in FIG. 6) whose longitudinal direction is perpendicular to the direction of vibration of the semiconductor chip 20.
As shown in FIG. 7A, for a bonding pattern 12 disposed so that the longitudinal direction is parallel with the direction of vibration for the ultrasonic vibration, even if ultrasonic vibration is applied, the bonding pattern 12 resists excitation, and accordingly when flip-chip bonding is carried out, the required frictional force is achieved between the bump 22 and the bonding pattern 12, resulting in increased strength for the bond between the bump 22 and the bonding pattern 12. On the other hand, as shown in FIG. 7B, for a bonding pattern 12 disposed so that the longitudinal direction is perpendicular to the direction of vibration of the ultrasonic vibration, the bonding pattern 12 is susceptible to moving so as to track the ultrasonic vibration, resulting in decreased strength for the bond between the bump 22 and the bonding pattern 12.
In this way, when semiconductor chips are mounted using ultrasonic vibration, to solve the problem of decreased strength for bonds between bumps and bonding patterns disposed with the lengthwise direction perpendicular to the direction of vibration for the ultrasonic vibration, a method (see Patent Document 1) where dummy patterns extend from the bonding patterns in the direction in which the ultrasonic vibration is applied and a method (see Patent Document 2) where via holes are formed on each side of the bonded parts where the bumps are bonded or filled vias are formed below the bonded parts have been proposed.
Patent Document 1
Japanese Laid-Open Patent Publication No. 2004-311637
Patent Document 2
Japanese Laid-Open Patent Publication No. 2002-94241
The method where protrusion patterns extend from the bonding patterns described above in a direction in which ultrasonic vibration is applied increases the strength of the bonds between the bonding patterns and the base layer and makes the bonding patterns resistant to excitation when the ultrasonic vibration is applied, resulting in increased strength for the bonds between the bumps and the bonding patterns. However, a method where the protrusion patterns are disposed simply corresponding to the positions on the bonding patterns at which the bumps are bonded is not thought to be effective in view of the case where the bonding patterns resonate due to the ultrasonic vibration applied to mount the semiconductor chip.
With the method where the formation positions of the via holes are adjusted relative to the bonding patterns, there are the problems that the construction of the circuit board becomes complex and limitations are placed on the designs of components due to the via holes being formed at predetermined positions.